A specific lambda value must be provided as a mean for optimum exhaust gas conversion. In current exhaust gas systems, as featured by the internal combustion engine described above, the measuring signal of the first exhaust gas probe upstream of the catalytic converter is used as a reference variable (controlled variable) for the lambda control. The measuring signal of the second exhaust gas probe downstream of the catalytic converter is used in a trim regulation to correct the lambda control. The trim regulation here serves to monitor the catalytic conversion and fine regulation of the fuel/air mixture. The trim regulation here is generally made up of a P regulator component and an I regulator component. The I regulator component here is intended to compensate for a lasting system deviation produced by displacements of the characteristic curves of the first exhaust gas probe. Such displacements of characteristic curves can result from ageing and/or dirt. The I regulator component is also designed to be correspondingly slow so as not to react to short-term problems (for example tank venting).
Where the characteristic curve is subject to sudden changes (e.g. contamination, after a probe change or after deletion of the adaptation values) the I component will only correct the deviation slowly. During this period the P component has to correct the system deviation. In contrast to the I component the P component is however only included in the calculation in certain operating states. This means that a characteristic curve displacement is not continuously corrected, resulting in an increase in emissions.
Sudden or rapid changes to the system deviation can therefore only be learned and adapted during a longer trip. Increased emissions must be assumed during this time.
An internal combustion engine of the type described in the introduction is known from DE 10 2008 018 013 B3. To eliminate the problem set out above it is proposed in this publication that the P component of the trim regulator should be observed and if the P component exceeds (in the case of positive regulator intervention) or drops below (in the case of negative regulator intervention) an applicable threshold for the duration of an air mass integral or a period, the I component should be compulsorily adjusted. To this end an amount dependent on the P component or the voltage of the second exhaust gas probe is added to the I component. This allows rapid adjustment of the I component to be achieved in the event of major regulator deviations. However the functionality tends toward overshooting. The non-linearity of the characteristic curve of the second exhaust gas probe and ageing effects mean that the association between the probe voltage and the actual deviation of the central position of the mixture is difficult to determine. Relatively major errors occur with small to medium deviations. The neutral position can therefore only be roughly achieved when there is a sudden adjustment of the I component.